1. Field of the Invention
The present invention relates to a combustion system for a vehicle, and more particularly, to a combustion system for a vehicle that reducing particulate matter and nitrogen oxide (NOx) of exhaust gas.
2. Description of Related Art
Generally, the exhaust gas of a diesel engine includes particulate matter and nitrogen oxide. However, the main component of the particulate matter, that is, soot, can be reduced at a high temperature in an oxygenation state, and the nitrogen oxide is mostly generated in a high temperature area.
An exhaust gas recirculation (EGR) system that recirculates exhaust gas into a combustion chamber is used to eliminate the nitrogen oxide.
That is, as the exhaust gas concentration becomes higher in the combustion chamber, the combustion temperature is decreased to reduce the nitrogen oxide. However, as the recirculation of the exhaust gas is increased, there is a problem that the oxygen concentration is decreased to increase particulate matter.
Techniques for stratifying the exhaust gas have been researched so as to resolve the above problem. That is, as the recirculation exhaust gas is stratified in the combustion chamber, the nitrogen oxide is reduced in an exhaust gas dense area of the combustion chamber and the soot that is generated from the exhaust gas dense area is oxidized in an oxygen dense area such that the two harmful exhaust materials that are in trade-off relationship can be simultaneously reduced.
Generally, when one combustion groove is formed in a piston, the concentration of the recirculation exhaust gas are max 34.7% and min 28.9% in a case in which 100% air is supplied from a first intake port and 60% recirculation exhaust gas is supplied from a second intake port, and therefore the difference of the concentration is little.
Accordingly, there is a problem in which the stratification of the recirculation exhaust gas is hardly achieved. The reason why the stratification of the recirculation exhaust gas is hardly achieved is that the dense area of the recirculation exhaust gas and the oxygen dense area that are separated at an early stage of a compression stroke are promoted to be mixed with each other by a squish flow at a last stage of the compression stroke.
Further, the conventional stratification technique stratifies the exhaust gas concentration toward the edge from the center portion of the combustion chamber, and therefore the gas of the center portion is mixed to the edge portion by the fuel that is injected from the center to the edge before ignition such that the stratification efficiency is reduced.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.